Can one hour in a dermatologist's office do more than eons at the gym? Here, a report on the new wave of extreme-temperature fat blasters

I've always assumed that if I ever bit the bullet and went in for liposuction, or even one of its newer, nonsurgical body-slimming cousins, it would be a last resort, reached after months of unsuccessful dieting and heinous workouts, that I would justify to myself (and my husband, mother, etc.) with the knowledge that "there was no other way" and "it had to be done." As it turned out, last summer I celebrated my impending metamorphosis with a cheeseburger and yet another canceled training session. Lying in the Upper East Side office of dermatologist Macrene Alexiades-Armenakas, MD, PhD, waiting for Zeltiq CoolSculpting (a process about which I had bothered to learn exactly nothing ahead of time) to erase—or at least significantly downsize—the gentle hillock below my belly button, I thought, Huh. How did I come to the decision to permanently deep-freeze a chunk of my own cells? It went something like this: Alexiades said, "So, I have this fat-freezing device…." I'm not sure I even let her finish the sentence.

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In the age of stem cell–derived supercreams and radio-­frequency skin-tightening gizmos, tackling beauty woes with the use of heat and cold seems downright Paleolithic, like asking Wilma Flintstone for hairstyle advice. But extreme temperatures, heat in particular, have long been the bedrock of all sorts of cosmetic tinkering. These days, most of the plumping, smoothing, and tightening that is not delivered via needle is executed with lasers, and these, by and large, work by heating skin, thus damaging old collagen and stimulating new collagen growth. Now, though, ever more high-tech applications of hot and cold are working below the neck (and below the skin, for that matter), blasting away belly bulge and slimming limbs. "When you're dealing with fat," says Alexiades, "it turns out you can accomplish the destruction of fat cells using either heat or cold."

Zeltiq CoolSculpting, for example, is a one-hour, no-fuss, no-muss fat-cell-destroyer that requires neither healing time nor a single stitch—or even, say, the formality of alerting one's spouse to the fact that you are "having something done."

Alexiades says the impetus for using cold to defat has its roots in the early '70s, when some papers were published about a condition dubbed "equestrian cold panniculitis." A handful of female horseback riders found that after long rides in the cold, "their thighs would freeze and their fat would become inflamed and, ultimately, disappear," she says. This wasn't just weight loss resulting from a good, hard workout—it occurred because fat cells, it seems, die off at temperatures that muscle and skin are able to withstand. But there's a reason it took decades for science to harness that revelation. "It has to be done in a very controlled fashion, at certain temperatures, to a point where you're going to get destruction of the fat without destruction of the surrounding tissue," says New York City dermatologist Roy Geronemus, MD, who was involved in several rounds of Zeltiq trials.

During a Zeltiq session, a molded cup is placed over the lower stomach or love handles; heavy-duty suction pulls pudge inside the cup, where it's chilled to 5˚C (41˚F). Some of the fat cells in the selected area are destroyed and ultimately disposed of by the liver, a process that, in all, can take four to six months. "Zeltiq was able to definitively demonstrate a minimum of 25 percent reduction in the fat that fits in the cup for treatment," says Alexiades. "That's a very high level of efficacy."

At Alexiades' office, her friendly, unflappable technician Malisa applied a cold, slimy sheet of protective gel across my lower stomach to shield the surface of my skin; lined up the machine's oblong handpiece on top of this, about an inch below my belly button; and turned on the device. Suction? Well, for a touch-and-go moment, I feared that my, er, roll wasn't the only thing that would be sucked into the device—it seemed entirely feasible that the rest of my body, and Malisa along with it, would somehow follow suit. After about seven minutes, though, we were both still there, and my stomach had grown numb. I felt next to nothing for the next 53 minutes and clicked calmly away on my BlackBerry until Malisa reappeared, powered down the machine, and popped off the suction cup. Horror: My flesh, embarrassingly malleable, had behaved like Jell-O in the mold of the device, and it was now frozen in the shape of a cold, pink, lifeless brick, distinct from the rest of my abdomen. Malisa briskly set about massaging this new topographical feature, and within a few seconds my body had meekly reaccepted it. Minutes later, I was back on the hot summer sidewalk, with a still-numb belly lying cold and surreal beneath my thin skirt and a mind ringing with Malisa's parting words: "Wait till you see it in three or four months," she said. "You're going to love it."

Cold Front

The Germans have a word for people like me: Warmduscher. Translation: "man who takes hot showers," or, in other words, a wimp. This is one insult to which I'll proudly answer. Polar bear swims, icy plunge pools, even tepid showers—these are forms of masochism, in my opinion. So Whole-Body Cryotherapy, which is not a life-after-death experience but rather a freestanding cylinder you step inside for a rapid, head-to-toe ice-down? Sounds like a bad idea to me. Developed in Japan in 1978, WBC has been used for years in Europe to treat chronic aches and pains by reducing inflammation. Now it's making its way into American spas and medical centers, as well as the locker room of the NBA's Minnesota Timberwolves. Sessions last only two and a half to three minutes, during which time liquid nitrogen gas plunges the temperature to between -200 and -250˚F. (Consider that Antarctica's record low, set in 1983, is a comparatively balmy -129˚F.) But the rapid chill penetrates only half a millimeter deep, causing vasoconstriction but not, say, frostbite; it reduces soreness and swelling, promoting what its practitioners call "parasympathetic rebound"—i.e., it takes the edge off postgame fatigue.

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Question is, will WBC make you skinnier? Don't rule it out. A study published earlier this year in The Journal of Clinical Investigation found that brown fat—that is, the good kind—can be activated by, yes, cold. Brown fat was long thought to exist only in mice and human newborns (as they can't shiver, it's what keeps them warm), but, beginning in 2009, it was detected in human adults as well. Unlike its lazy, energy-storing white counterpart, the brown stuff is located in small, oddly placed patches—a few ounces in the upper back, on the side of the neck, between collarbone and shoulder, along the spine—and it burns calories like a Jillian Michaels devotee, especially when we're chilly. In the study, male subjects who were held in a room that was cool, but not cold enough to cause shivering, burned an average of 250 calories over three hours—80 percent more than they would have normally.

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Rather unfairly, people who don't have weight problems tend to be the ones with the most brown fat, and until recently we had little idea of how one could gain more of it. (McDonald's fries, sadly, don't help in this arena.) Now scientists at the Dana-Farber Cancer Institute in Boston have discovered a new hormone, irisin, which converts white fat cells into brown fat cells. And it seems that the same thing that helps banish white fat is what also helps make more brown: Exercise tells the body to release more irisin, which in turn causes more fat cells to be transformed. So far, the effect has been documented only in rodents, but human irisin is identical to that of mice, so there's a good chance our bodies do the same thing. Notably, the irisin-generated brown fat was of a different type from the cold-activated kind targeted in the JCI study. Nevertheless, it might be reason enough to book next winter's ski getaway now—increasingly, it appears that exercise in the cold could prove to be the best fat-blaster of all.

Heat Wave

On the opposite end of the thermometer, dermatologists have set their dials to 62˚C (143.6˚F). This, according to Alexiades, is the temperature at which optimal collagen injury occurs—and skin improvement can begin. "Until now, everything we were doing for skin tightening and wrinkle reduction was guesswork," she says. "We were guessing that we were putting enough heat into the dermis." The skin-firming device du jour, ePrime, is changing all that: Its handpiece is studded with five pairs of hair-thin needles, which bypass the skin's superficial layers to go directly into the dermis and deliver heat at a steady, measurable temperature. A recent convert, Manhattanite Susan D., whose defined cheekbones and taut jawline speak to both her genetics and the subtle ministrations of "Dr. A," was thrilled with her ePrime tune-up and reported that the device's benefits outweigh its bite. "Most of it didn't hurt at all," she says. "But when it hits an area that's not fully anesthetized, you definitely feel the heat."

ePrime has been proven safe for the face and neck, "but the next horizon is the body," says Alexiades, who sees it shoring up sagging knees and loosey-goosey elbow skin in the not-too-distant future. On those telltale areas, "I've tried Thermage. I've tried Titan," she says. "The results are okay—they're not terrific."

For now, though, the hot competitor to fat-freezer Zeltiq is the new Liposonix, a gadget that liquefies fat using high-intensity, focused ultrasound (a different version of the technology used in the face-firming Ulthera). The manufacturers of Liposonix don't make claims about specific weight loss, but they do have a catchy tagline: "One treatment, one hour, one size smaller." On average, patients lose an inch around the waistline after one session. Lipo­sonix heats fat to 55˚C, the temperature at which it melts (and the same temperature that "smart lipo" procedures use to assist fat extraction with a cannula), which "stimulates our immune system to come in and eat up the damaged fat cells and take that damaged fat to the liver," says dermatologist Anne Chapas, MD. "Then the body gets rid of it." She says some patients see results within four to six weeks; most require seven to 12.

"I've had people call me up and say, 'Can I get Liposonix on my full body?' " Chapas says. In a word, no. Liposonix was FDA-approved in November for the abdomen and flanks. To get what you want out of it, "you have to be able to pinch an inch," she says, but you can't have a BMI of more than 30, the cutoff for obesity. "Neither [Zeltiq or Liposonix] is for someone who is obese and wants to lose weight," says Chapas, who performs both procedures. "You have to be pretty happy in the skin you're in, and really just trying to lose, you know, little problem areas."

As for my own Zeltiq zapping, nearly a year later, the jury is still out. Sometimes I'm convinced it worked. But fat is fickle—as are hormonal shifts and bewitching slivers of chocolate cake. You're up, you're down; the jeans fit, they don't. Unless you're a slim woman with a specific drives-you-nuts problem area (and I'm more of a curvy-all-over type), you're looking for a relatively subtle change in the one area of a woman's body where it would be the most difficult to observe. For many people, a 25 percent loss with Zeltiq or the one-inch subtraction of Liposonix equals a skirt size, maybe a belt loop or two; for others, it's negligible.

Which is not to say that I've ruled out miracles, even slightly scary-sounding ones. "It's not heat, it's not cold—it's chemical!" says Alexiades of the new magic bullet that she's investigating: injections of something called ATX101, or deoxycholate, a natural substance found in the human body, which works on the metabolism of fat cells to dissolve fat. As of yet, it's only in phase-II clinical trials, but Alexiades has high hopes. "Now that we're moving at such a rapid pace, liposuction, in my view, is going to be obsolete. All you're going to have to do is inject a solution to dissolve fat. That's the future."